1. Field of the Invention
The present invention relates to a method of developing in the presence of a development nucleator photographic light-sensitive silver halide materials for the formation of direct-positive images having a satisfactory maximum density with a hydroquinone-type developing solution having a pH-value not higher than 12.0.
In silver halide photography a photographic method, according to which a positive image is made without the use of a negative image or an intermediary process producing a negative image, is called a direct-positive method. A photographic light-sensitive material and a photographic emulsion for use according to such photographic method are called direct-positive material and direct-positive emulsion respectively.
A variety of direct-positive photographic methods are known. The most useful methods are the method, which comprises exposing prefogged silver halide grains to light in the presence of a desensitizing agent and developing them, and the method, which comprises subjecting a silver halide emulsion containing silver halide grains that have light-sensitive specks mainly inside the grains to an image-wise exposure and developing the exposed emulsion in the presence of a development nucleator. The present invention relates to the latter method. A silver halide emulsion comprising light-sensitive specks mainly inside the grains and which forms latent images mainly inside the grains is referred to as internal latent image-type silver halide emulsion, and thus is distinguished from silver halide grains that form latent images mainly at the surface of the grains.
It is known to develop a latent image that has been formed mainly inside the grains by means of a so-called internal developer, but the method, material, and emulsions used in accordance with the present invention are not concerned with that type of development, but rather with the type of development using a so-called surface developer.
2. Description of the Prior Art
Methods for making a direct-positive image by development of an exposed internal latent image type-silver halide emulsion in the presence of a development nucleator by means of a surface developer, and photographic emulsions and photographic light-sensitive materials used in such methods have been disclosed in i.a. GB-A 1,011,062, 1,151,363, 1,195,837, in JA Patent Publication No. 29,405/68, and in U.S. Pat. Nos. 2,456,953, 2,497,875, 2,497,876, 2,588,982, 2,592,250, 2,675,318, 3,227,552, 3,761,276, 4,540,655.
In the internal latent image-type method for making a direct-positive image, the development nucleator may be incorporated into a developing solution, but it is usually incorporated into the photographic emulsion layer or in another layer of the photographic light-sensitive material, the development nucleator being adsorbed at the surface of the silver halide grains. Development nucleators that can be used in the above-described method for making a direct-positive image include hydrazine and derivatives thereof as described in i.a. "Zeitschrift fur Wissenschaftliche Photographie" by Arens, vol. 48, (1953) p. 48, DD-A 5024, DE-A 3,021,423, and in U.S. Pat. No. 2,563,785, 2,588,982, 3,227,552, 4,245,037, 4,374,923, 4,540,655, in Research Disclosure 23,510, p. 346-348 and the documents referred to therein.
The fogging action of development nucleators in internal latent-type silver halide emulsions is triggered only when the pH of the developing solution used is sufficiently high i.e. at least 11. To reach satisfactory results in particular with respect to Dmax it is customary to increase the pH to values as high as 12 to 13. However, an increase of the pH of the developing solution to such high values leads to an increased susceptibility of the solution to aerial oxidation. The oxidation products give rise to substantial changes in the photographic characteristics especially a reduced Dmax.